如何在custon select中启用optgroup

Question

我正在使用此代码来设置选择选项下拉菜单的样式。它使用javascript，以便可以使用CSS编辑外观。 它运行良好，但问题是它禁用了optgroup的标签。我再也看不到选项组标题了，最重要的是，我需要有两个连续的标签，并且比选项要多。我尝试了很多方法。使用残障人士的意见，它是有效的，但只是一种选择，因为以前的残障人士的意见将消失。 我该怎么办？

<div class="custom-select" style="width:200px;">
    <select>
     <optgroup label="select something">
     </optgroup>
      <optgroup label="German Cars">
       <option value="mercedes">Mercedes</option>
       <option value="audi">Audi</option>
     </optgroup>
     <optgroup label="German Cars">
      <option value="0">Select car:</option>
      <option value="1">Audi</option>
      <option value="2">BMW</option>
      <option value="3">Citroen</option>
      <option value="4">Ford</option>
      <option value="5">Honda</option>
      <option value="6">Jaguar</option>
      <option value="7">Land Rover</option>
      <option value="8">Mercedes</option>
      <option value="9">Mini</option>
      <option value="10">Nissan</option>
      <option value="11">Toyota</option>
      <option value="12">Volvo</option>
    </optgroup>
   </select>
 </div>

    <script>
    var x, i, j, selElmnt, a, b, c;
    /*look for any elements with the class "custom-select":*/
    x = document.getElementsByClassName("custom-select");
    for (i = 0; i < x.length; i++) {
      selElmnt = x[i].getElementsByTagName("select")[0];
      /*for each element, create a new DIV that will act as the selected item:*/
      a = document.createElement("DIV");
      a.setAttribute("class", "select-selected");
      a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML;
      x[i].appendChild(a);
      /*for each element, create a new DIV that will contain the option list:*/
      b = document.createElement("DIV");
      b.setAttribute("class", "select-items select-hide");
      for (j = 0; j < selElmnt.length; j++) {
        /*for each option in the original select element,
        create a new DIV that will act as an option item:*/
        c = document.createElement("DIV");
        c.innerHTML = selElmnt.options[j].innerHTML;
        c.addEventListener("click", function(e) {
            /*when an item is clicked, update the original select box,
            and the selected item:*/
            var y, i, k, s, h;
            s = this.parentNode.parentNode.getElementsByTagName("select")[0];
            h = this.parentNode.previousSibling;
            for (i = 0; i < s.length; i++) {
              if (s.options[i].innerHTML == this.innerHTML) {
                s.selectedIndex = i;
                h.innerHTML = this.innerHTML;
                y = this.parentNode.getElementsByClassName("same-as-selected");
                for (k = 0; k < y.length; k++) {
                  y[k].removeAttribute("class");
                }
                this.setAttribute("class", "same-as-selected");
                break;
              }
            }
            h.click();
        });
        b.appendChild(c);
      }
      x[i].appendChild(b);
      a.addEventListener("click", function(e) {
          /*when the select box is clicked, close any other select boxes,
          and open/close the current select box:*/
          e.stopPropagation();
          closeAllSelect(this);
          this.nextSibling.classList.toggle("select-hide");
          this.classList.toggle("select-arrow-active");
        });
    }
    function closeAllSelect(elmnt) {
      /*a function that will close all select boxes in the document,
      except the current select box:*/
      var x, y, i, arrNo = [];
      x = document.getElementsByClassName("select-items");
      y = document.getElementsByClassName("select-selected");
      for (i = 0; i < y.length; i++) {
        if (elmnt == y[i]) {
          arrNo.push(i)
        } else {
          y[i].classList.remove("select-arrow-active");
        }
      }
      for (i = 0; i < x.length; i++) {
        if (arrNo.indexOf(i)) {
          x[i].classList.add("select-hide");
        }
      }
    }
    /*if the user clicks anywhere outside the select box,
    then close all select boxes:*/
    document.addEventListener("click", closeAllSelect);
    </script>